1. Field of the Invention
The invention relates to a fuel cell generating set, and more particularly to a fuel cell generating set including a Lysholm compressor for compressing air for a fuel cell. For instance, the generating set in accordance with the invention can be applied to an electric automobile.
2. Description of the Prior Art
Nowadays, an Otto cycle or Diesel cycle internal combustion engine has been used as an automobile engine. They are compact, but ZEV (zero emission vehicles) such as an electric automobile are expected to develop from the standpoint of regulation of exhaust gas such as NO.sub.x, fine particles, CO and CO.sub.2. As example of ZEV, fuel cell vehicles and battery-powered vehicles are now being developed in several countries.
FIG. 1 is a block diagram of a conventional fuel cell automobile. The illustrated automobile includes a fuel tank 1, a fuel processing device 2, a fuel cell 3, a battery 4, a power controller 5, a motor 6 for driving a drive shaft, and a wheel driving mechanism 7. Fuel such as methane and methanol is stored in the fuel tank 1. The fuel processing device 2 reforms fuel stored in the fuel tank 1 into a fuel gas containing hydrogen therein. Receiving the thus reformed fuel, the fuel cell 3 generates electricity, by which the motor 6 is driven. Thus, wheels are driven by means of the wheel driving mechanism 7. The battery 4 is used as a starter, and the power controller 5 controls the operation of the automobile. The fuel processing device 2 may be omitted, in which case hydrogen gas stored in the tank 1 is directly supplied into the fuel cell 3.
In the above-mentioned conventional fuel cell automobile, it is necessary to operate a fuel cell under pressure and supply pressurized air at 3 to 4 atm. Into the fuel cell, in order to make the fuel cell smaller in size and enhance performance of the fuel cell. Thus, there is a need for an air source having a smaller air capacity, a higher pressure ratio, and a higher efficiency, to be used for a small-sized fuel cell system.
There has been conventionally employed a two-stage supercharger using a turbo-charger therein, as an air source for such a fuel cell system. However, two-stage compression has problems that in that it is unavoidable that the compressor complicated in structure, and efficiency is thus deteriorated. On the other hand, a Lysholm compressor could provide pressurized air having a compression ratio equal to or greater than 3 in a single compression type. However, when a Lysholm compressor is used in a fuel cell, there are problems to be solved, as follows.
Firstly, a Lysholm compressor provides a high efficiency in a usually used revolution range, however, volumetric efficiency is significantly deteriorated because of leakage between rotors, when a gas quantity used is quite small.
Secondly, temperature rise in air caused by single compression deteriorates temperature efficiency, and thus poses a problem that greater power is required to operate the Lysholm compressor.
Thirdly, a discharge temperature is beyond 200.degree. C. because of single compression. Thus, a rotor and a casing have to be made of iron or other similar materials, resulting in an increase in weight.